In die casting, molten metal is injected by a shot plunger into a fixed-volume cavity defined by die sections. Air displaced from the die cavity by the cast metal is vented through a conduit in the die. Alternately, the conduit may be connected to a vacuum source to evacuate the cavity prior to casting, thereby further reducing gas entrapment in the casting.
It is known to incorporate into the conduit a valve having an open position for gas venting and a closed position to prevent the escape of cast metal through the conduit. U.S. Ser. No. 174,572, filed by Priem on Mar. 29, 1988, describes an axial impingement type of valve for this purpose wherein valve closure is actuated by impingement of cast metal against a valve head. A pneumatic pulse may be provided to assist in triggering the closure of the valve. This valve has not been entirely satisfactory for casting large products that require a massive, multi-sectional die, such as automotive automatic transmission housings that may weigh more than 35 pounds. The valve is adapted to be located near the die periphery. This location results in an extended conduit that increases the amount of scrap metal for each casting. Furthermore, within the environment of a large die casting operation, a valve of the axial melt impingement type is prone to malfunction and requires frequent maintenance and repair. A second common type of valve for a die casting gas venting system comprises a valve head connected to a hydraulic cylinder. The hydraulic cylinder opens or closes the valve in response to signals dependent upon predetermined points during the casting cycle. While the fluid-actuated valve is reliable to assure timely closure and avoid catastrophic metal escape, such valves have also been designed to be mounted near the die periphery for suitable connection to the fluid cylinder and have featured a limited valve opening insufficient to accomodate the flow of gas from the large die cavity within the allotted cycle time.
Therefore, it is an object of this invention to provide an improved valve for a die casting gas venting system, which valve opens and closes in response to fluid pressure and features a compact design suitable for convenient incorporation into a die body, including, for example, within the interior of a massive die required for large castings.